Examine source code of 3001 Redirect

{
  "manifest_version": 2,
  "name": "3001 Redirect",
  "version": "0.1",
  "description": "Redirects 500 errors on localhost to port 3001",
  "icons": {
    "48": "icons/border-48.png"
  },
  "content_scripts": [
    {
      "matches": [
        "*://*.localhost/*"
      ],
      "js": [
        "3001redirect.js"
      ]
    }
  ]
}